1. Field of the Invention
The present invention relates to a paper feeder for feeding, one by one, sheets stacked together which is for use in an image forming apparatus or the like for forming images on sheets.
2. Description of the Related Art
A conventional paper feeder for use in image forming apparatuses adopts a slope surface separation system in which separation of sheets is effected by utilizing a slope surface. In the slope surface separation type paper feeder, a slope surface is provided at the forward end of the stacked sheets, and a paper feeding roller contacts the uppermost sheet to deliver it, the delivered sheet abutting the slope surface, whereby the sheets are separated from each other.
Usually, this slope surface separation type paper feeder is used when delivering sheets stacked horizontally. However, by inclining the sheet stacking surface, the installation area of the image forming apparatus can be reduced, and the apparatus size can be reduced, so that it is to be considered appropriate to apply the slope surface separation system to this inclined structure.
An example in which the slope surface separation system is applied to a paper feeder in which the sheet stacking surface is inclined will be described with reference to FIGS. 14 and 15. In the drawings, numeral 101 indicates a sheet stacking surface on which sheets S are to be placed, and numeral 102 indicates a paper feeding roller integrally holding a gear (not shown). Numeral 103 indicates an idler gear A in mesh with the gear of the paper feeding roller, numeral 104 indicates an idler gear B in mesh with the idler gear A 103, numeral 105 indicates a drive shaft, and numeral 106 indicates a drive gear fastened to the drive shaft 105 and in mesh with the idler gear B. Numeral 107 indicates a paper feeding roller arm rotatably holding the paper feeding roller 102 and the idler gears 103 and 104 and rotatably held by the drive shaft 105.
Numeral 108 indicates a separation slope surface which supports the sheets and which is at an angle xcex8 with respect to the sheet stacking surface 101, numeral 109 indicates a lower guide which is integral with the separation slope surface 108 and which guides the lower side of the sheets fed, and numeral 110 indicates an upper guide for guiding the upper side of the sheets. Numeral 111 indicates a conveying roller which rotates to thereby apply to the sheets fed a conveying force for guiding the sheets in a predetermined direction, and numeral 112 indicates a rotatable conveying roller arranged opposite to the conveying roller 111. Numeral 113 indicates a roller holder which rotatably holds the conveying roller 112 and which is held by the upper guide, etc., and numeral 114 indicates a conveying spring which biases the roller holder 113 and which presses the conveying roller 112 against the conveying roller 111.
Numeral 115 indicates a conveying guide for guiding the lower side of the sheets between the paper feeding and the fixing unit. Numeral 116 indicates a toner cartridge, numeral 117 indicates a development drum in the toner cartridge, numeral 118 indicates a transfer roller which is pressed against the development drum 117 and rotates and which transfers the toner image on the development drum 117 to the sheet, numeral 119 indicates a fuser for fixing the toner image to the sheet, numeral 120 indicates a heating device for heating the toner and sheet in the fuser 119, and numeral 121 indicates a fixing roller which rotates as it presses the sheet against the heating device 120 to convey the sheet.
Numeral 128 indicates a scanner for writing the latent image on the development drum 117 by a laser beam or the like, numeral 129 indicates an optical stand securing the scanner in position, and numeral 130 indicates an electrical portion formed by a power source for the entire image forming apparatus, a control circuit, etc.
Numeral 122 indicates a paper discharge roller pair A for conveying the sheet after fixing, numerals 123 and 124 indicate an upper paper discharge guide and a lower paper discharge guide for guiding the sheet conveyed by the discharge roller pair A, numeral 125 indicates a paper discharge roller B for discharging the sheet guided by the paper discharge guides 123 and 124 to the exterior of the image forming apparatus, numeral 126 indicates a rotatable paper discharge roller pressurized toward the paper discharge roller B 125, and numeral 127 indicates a paper discharge tray on which the sheets discharged are stacked.
The paper feeding operation of the paper feeder constructed as described above will now be described.
The drive shaft 105 is driven by a controllable drive mechanism (not shown). As a result, the starting and stopping of the paper feeding operation is controlled. When starting paper feeding, the drive shaft 105 is driven by a drive mechanism (not shown) and rotates. This rotation is transmitted through the idler gear B 104 and the idler gear A 103 to the paper feeding roller 102, and the paper feeding roller 102 starts to rotate. The paper feeding roller arm 107 holding the paper feeding roller 102 so as to be rotatable around the drive shaft 102 is biased so as to rotate counterclockwise as seen in the drawing by a biasing means (not shown) or by its own weight, and, by this biasing force, the paper feeding roller 102 is slightly in press contact with the upper surface of the uppermost sheet S1 of the pile of sheets S stacked on the sheet stacking surface.
Thus, by starting rotation of the paper feeding roller 102, a feeding force F due to frictional force is applied to the sheet S1. The sheet S1 receives a reactive force F2 from the separation slope surface 108; due to this reactive force F2, the sheet S1 is bent, whereby the sheet S1 moves on the separation slope surface 108, with its forward end portion abutting and being bent.
The proceeding direction of the sheet S1 is determined by the upper guide 110 and the lower guide 109, and it enters a nip defined by the conveying roller 112 biased toward the conveying roller 111, and, by the rotation of the conveying roller 111, it is further fed downward with respect to the sheet conveying direction.
The sheet S1 is then guided by the conveying guide 115 and fed to the nip between the development drum 117 and the transfer roller 118. The latent image written to the development drum 117 by the scanner 128 is developed in the toner cartridge 117 and transferred to the sheet by the transfer roller 118. The toner transferred to the sheet is fixed in the fuser to the sheet, and the sheet to which the image has been fixed is stacked on the paper discharge tray 127 outside the image forming apparatus by the paper discharge roller pair A 122 and the paper discharge roller B 125.
The above-described conventional apparatus has the following problems.
If, when inserting a pile of sheets S in the paper feeder for the purpose of supplying sheets, etc., the pile of sheet is put in by firmly abutting it against the separation slope surface 108 along the sheet stacking surface 101 or by causing it to drop in by its own weight, the forward end portion of the pile of sheets S abuts the separation slope surface 108 and is bent (buckles) as shown in FIG. 15. When the forward end portion of the pile of sheets S is thus bent, a plurality of sheets begin to deform simultaneously at the time of paper feeding, resulting in duplicate or multifold feeding.
Further, the sheets other than the uppermost sheet are influenced by frictional force when the uppermost sheet is fed, so that, by repeating the paper feeding operation, part of the pile of sheets S is bent as shown in FIG. 15, resulting in multifold feeding. This often happens near the boundary between the pile of sheets S, which has been reduced in volume as a result of paper feeding, and another pile of sheet newly supplied and placed thereon.
The present invention has been made in view of the above problems. Accordingly, it is an object of the present invention to provide a paper feeder of the type which has a sheet stacking surface obliquely holding a pile of sheets and which adopts the slope surface separation system, wherein no such inconvenience as multifold feeding is involved even when the pile of sheets is forcibly put in the paper feeder or caused to drop in it by its own weight at the time, for example, of supplying sheets.
In accordance with these objects, there is provided a paper feeder comprising a sheet stacking surface on which sheets are stacked, paper feeding means for feeding the sheets stacked on the sheet stacking surface, the paper feeding means in contact with an uppermost sheet of the sheets stacked on the sheet stacking surface, and a movable separation slope surface arranged such that a leading end of the sheets stacked on the sheet stacking surface abuts the movable separation slope-surface, the movable separation slope surface being rotatable between a first position and a second position that differ in inclination angle made by the movable separation slope surface and the sheet stacking surface. Driving means are also provided for rotating the movable slope surface between the first position and the second position.
In accordance with another object of the present invention there is provided an image forming apparatus containing a paper feeder as described above and image forming means for forming images on sheets fed from that paper feeder.
Further, in a structure in which a rotatably supported roller is provided at the end of the movable separation slope surface farther from the sheet stacking surface, it is possible to mitigate the resistance offered to the sheets conveyed with its forward end sliding when the movable separation slope surface is in the second position.
Further, when the movable separation slope surface is not moved to the second position in a first paper feeding operation by the paper feeding means, and the movable separation slope surface is moved from the first position to the second position in a second paper feeding operation, it is possible to effect setting such that the possibility of multifold feeding is further reduced when a sort of sheets which require small paper feeding force for passing the movable separation slope surface are caused to flow in a large amount.
Further, when control is effected such that the timing for starting the paper feeding means is delayed as compared with the timing for starting the movable separation slope surface, the uppermost sheet is temporarily separated from the pile of sheets below it with a smaller force before the starting of the paper feeding means, thereby making it possible to restrain the occurrence of multifold feeding.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.